The above-identified co-pending application Ser. No. 08/709,062 now U.S. Pat. No. 5,796,214 discloses and claims a ballast circuit for a gas discharge lamp. The ballast circuit includes a d.c.-to-a.c. converter formed of a pair of serially connected switches having opposite conduction modes. For instance, one switch may be an n-channel enhancement mode MOSFET, and the other, a p-channel enhancement mode MOSFET, with their sources interconnected at a common node. This allows a single control voltage applied to the gates, or control nodes, of the MOSFETs, to alternately switch on one MOSFET and then the other. The gate drive circuitry disclosed employs a bidirectional voltage clamp implemented by a pair of back-to-back connected Zener diodes.
The present inventor has discovered a new configuration for a bidirectional voltage clamp, which allows for higher speed operation and more reliable lamp starting.